The Immune Assessment Core (IAC) will be based at the Childrens Hospital Los Angeles (CHLA) and will provide immune evaluations of transplant recipients on multi-center or groupwide clinical trials. The IAC will be a virtual core with specific assays done at multiple sites: immunophenotyping of both recipient peripheral blood leukocytes and the HSC products at each clinical site; TREC assays at the NIH under Dr. Douek; antigen specific T lymphocyte blastogenesis to environmental DNA viruses at CHLA; and cytokine production at the Dana Farber Cancer Institute under Dr. Eva Guinan. In Year 2 the assessment of Class II tetramer binding, produced by Core E, will form part of the routine immune assessment: the first tetramers to be produced will be CMV pp65. The Core will also assess the immune response of HSCT recipients to timed immunization after HSCT with Hepatitis B, diphtheria toxoid conjugated pneumococcal and tetanus toxoid vaccinations. The patients' cellular and humoral responses will be determined. The antigenic repertoire of the T lymphocytes, which develop antigen specific function to either environmental antigens or vaccinations, will be evaluated by a matrix of overlapping peptides to define their repertoire breadth. Patients in the clinical trials will be compared to control patients evaluated during the first year of the grant. The Core at CHLA will be responsible for developing and overseeing a QA/QC program as well as the QA of reagents. The IAC will be responsible for integrating new immune assays into groupwide evaluations and modifying the immunophenotyping panels based upon results from the individual Projects.